1. Field of the Invention
The present invention relates to a high-capacity optical recording medium for storing data, and more particularly to a recordable high-capacity optical disc such as recordable high-capacity compact discs and recordable digital video discs.
2. Discussion of the Related Art
Currently, DVD-Rs (digital video disc-recordable) have been developed as next-generation high-capacity optical discs. In order to increase the recording capacity of DVD-Rs, the following technologies are needed:
(1) recording materials in which relatively small recording pits can be formed; PA1 (2) advanced image compression technologies such as MPEG2 (Motion Picture Experts Group); and PA1 (3) a laser diode emitting light having a relatively short wavelength for reading relatively small pits. PA1 (1) recording media using a cyanine dye as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 57-82093, 58-56892, 58-112790, 58-114989, 59-85791, 60-83236, 60-89842 and 61-25886; PA1 (2) recording media using a phthalocyanine dye as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 61-150243, 61-177287, 61-154888, 61-24609, 62-39286, 63-37991 and 63-39888; PA1 (1) recording media using a cyanine dye and a light reflective metal layer as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 1-159842, 2-42652, 2-13656 and 2-168446; PA1 (2) recording media using a phthalocyanine dye and a light reflective metal layer as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 1-176585, 3-215446, 4-113886, 4-226390, 5-1272, 5-171052, 5-116456, 5-96860 and 5-139044; and PA1 (3) recording media using an azo chelate dye and a light reflective metal layer as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 4-46186, 4-141489, 4-361088, 5-279580, 7-51673, 7-161069, 7-37272, 7-71867, 8-231866, 8-295811, 9-277703, and 10-36693. PA1 (1) recording media using a combination of a CD-R recording material with an azo dye capable of absorbing light having a relatively short wavelength as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 8-156408, 8-310121, 9-39394 and 9-40659; PA1 (2) recording media using a combination of a CD-R recording material with an azaannulene dye capable of absorbing light having a relatively short wavelength as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 8-276662 and 8-287513; and PA1 (3) recording media using a combination of a CD-R recording material with another dye capable of absorbing light having a relatively short wavelength as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 8-169182, 8-310129 and 8-324117. PA1 (1) recording media using a cyanine dye and a light reflective metal layer as a recording material; and PA1 (2) recording media using an imidazole type azomethine dye and a light reflective metal layer as a recording material, which have been disclosed in Japanese Laid-Open Patent Publications Nos. 8-198872, 8-209012 and 8-283263.
As for the laser diodes emitting light in the red region, only AlGaInP laser diodes, which emit light having a wavelength of 670 nm, have been developed for commercial operation and used for bar code readers and measuring instruments. With the capacity of optical discs increased, red color laser diodes have been used in the optical data storage field. In a case of DVD drives, light within the 635 nm band or 650 nm band, which is emitted by laser diodes, is standardized as a light source. In order to perform high-density recording, it is desirable for the light used for high-density recording to have as short a wavelength as possible. Therefore, the light having a wavelength of 635 nm is preferably used for drives for recording information in recordable optical media. In contrast, as for the read-only DVD-ROM (digital video disc-read-only-memory) drives, drives using light having a wavelength of 650 nm are marketed.
Until now, the following write-once read-many-times information recording media (WORM) have been proposed:
The following background art concerning recordable compact discs (CD-Rs) has been proposed:
In addition, the following background art concerning recordable compact discs (CD-Rs), which can perform only reproduction in DVD system, has been proposed:
Further, the following background art concerning recordable high-capacity compact discs (DVD-Rs) has been proposed:
Under such circumstances, a medium, which can record and reproduce information with light having a wavelength of 635 nm and in addition can reproduce information with light having a wavelength of 650 nm, are most preferable as the DVD-R media. However, a DVD-R medium, which can record and reproduce information with an optical pickup using light having a wavelength not greater than 650 nm and which has good light resistance and good preservability, has not yet been developed.
The current CD-R disc systems are designed so that record and reproduction can be performed by laser light having a wavelength of from 770 nm to 790 nm. On the other hand, since CD-Rs use in the recording layer thereof a dye having maximum absorption in a wavelength range of from 680 nm to 750 nm and are designed so as to have high reflectivity against light in a wavelength range of from 770 nm to 790 nm by controlling their optical constants and layer thickness, CD-Rs have very poor reflectivity against light having a wavelength not greater than 700 nm. Therefore, a problem tends to occur in that information, which is recorded in a CD-R by the current CD-R systems and which can be reproduced by the CD-R systems, cannot be reproduced by DVD-R disc systems.
Because of these reasons, a need exists for an optical recording medium in which information can be recorded and reproduced by DVD-R disc systems and which has good light resistance and good preservability.